For as long as I can remember, I've known that water expands when it freezes. When I got to junior high physics, I learned that water is the only thing we know of that expands when it gets colder. And at some point, I forget when, I read about how ice skates work.

But to have Feynman say, "water expands when it freezes, so the pressure tries to undo the expansion and melts it" and get that Oh? Oh. Oh! feeling...